1. Field of Invention
The present invention relates to modulators, and more particularly to an improved spread spectrum BPSK, or Binary Phase Shift Keying, Modulation system designed for providing gain, low cost and suppressed carrier output, as well as compatibility with CMOS low power logic modulation drive circuitry. The present invention also teaches a Frequency Multiplier circuit, which is much less costly than traditional designs currently known.
The present system teaches a new, superior, and less costly BPSK modulator and/or frequency multiplier than that contemplated by the prior art, providing a less complicated system while outputting increased gain over prior art modulators.
2. Prior Art & General Background
Previous spread spectrum BPSK modulators required conventional balance mixers to produce carrier suppression. These conventional modulators utilized either 1) a complex transistor array in conjunction with a transformer tunable with a potonciometer or 2) two center tapped transformers and four diodes, which arrangement required a high level drive circuit to modulate it, typically +7 to +15 dBM.
Besides the greater expense, increased complexity thereby contributing the probability of failure, and incompatibility with low power -10 dB CMOS logic drive circuitry, the prior art modulators typically produced on the order of six dB of signal loss, resulting in considerably less satisfactory overall performance when compared to the present invention.
3. General, Summary Discussion of the Invention
A low cost spread spectrum modulator is an essential component of a commercially viable spread spectrum communications system. While a low cost, high performance modulator has not been contemplated until now, the present invention describes the ideal modulator, designed specifically for Binary Phase Shift Keying or BPSK.
The present invention is designed to provide a low cost, efficient, quality and reliable modulation system having sufficiently high BPSK modulation rate, coupled with the suppressed carrier output needed in spread spectrum communication systems and the like.
Unlike the prior art, which required balance mixers of the sort discussed in the background section supra, the present invention provides a BPSK modulator utilizing only one transformer having the capability of adjusting for maximum carrier suppression, in conjunction with two bipolar transistors, which allows the modulator to be driven from the low power logic levels found in CMOS circuitry -10 dBM. The present invention in its preferred embodiment produces eight dB of gain, much superior in performance over the prior art, which performs at a six dB signal loss.
Further, the present invention is not limited to utilizing two bipolar transistors as discussed supra and may utilize in an equivalent fashion any device which provides sufficient gain at the desired frequency or operation, as well as having sufficiently fast switching capabilities.
For example, other acceptable, equivalent devices which may be utilized in place of the two transistors in the present invention may include high frequency field effect transistors (FET's), or digital logic gates, which are biased into a linear region utilizing common techniques. These devices may be incorporated into the system of the present invention, replacing in effect the transistors, utilizing common engineering techniques.
The present invention, in an alternative use, may be utilized as a frequency multiplier. For example, if the transistor, or its equivalent, is adequately fast, for example, F.sub.t &gt;1 GHZ, the system may be utilized to create at its output a higher frequency harmonic.
As is known in the art, it is a common radio design practice to utilize a non-linear device such as a diode, transistor, or the like to perform frequency multiplication. This is desirable because only lower frequency crystals are readily available, and as such, the lower frequency must then be translated into the higher, desired frequency.
When the modulation transistor arrangement is additionally utilized in the present invention in the frequency modulation capacity, less subsequent stages are required. This serves to lower both the cost and complexity of a frequency multiplier system, when compared to the prior art systems.
It is thus an object of the present invention to provide a low cost, high quality BPSK modulator compatible for use in spread spectrum-type communications systems.
It is another object of the present invention to provide a BPSK modulation system which is compatible with low power logic input, such as that driven by CMOS circuitry.
It is still another object of the present invention to provide a BPSK modulator which utilizes a single transformer and two transistors, adjusts for carrier suppression, and provides eight db+ of gain.